Spectral Induced Polarization (SIP) is an electrical method used to map variations in the electrical properties of the earth. SIP is based on the fact that when an electric field is applied to the ground, electric current flows through the earth and charge separation takes place at mineral-fluid interfaces. In other words, the mineral-fluid interface becomes electrically polarized.
SIP systems are used in exploration, water resources and environmental industries to investigate the physicochemical properties of the earth. SIP systems use electrical measurements of earth materials to also estimate geochemical and biogeochemical processes in the subsurface; field applications of the SIP method are based on successful laboratory experiments.
Spectral Induced Polarization (SIP) is an accepted method for measuring the low frequency electrical properties of earth materials. The prior patent by Vinegar and Waxman (V&W) U.S. Pat. No. 4,359,687 issued Nov. 16, 1982 “Method and Apparatus for Determining Shaliness and Oil in Earth Formations Using Induced Polarization in the Frequency Domain” lays out a configuration of a sonde and borehole measurement system utilizing SIP. Vinegar and Waxman U.S. Pat. No. 4,583,046 issued Apr. 14, 1986 “Apparatus for the Focused Electrode Induced Polarization Logging” includes current focusing to improve resolution.
SIP borehole systems, like the ones described in the V&W patents, have numerous shortcomings. For instance, such systems have limited functionality because they require external connections for power, stimulus generation, data acquisition, data processing, data storage, and control. Additionally, the V&W systems electronics are dependent on the number of electrodes, geometrical electrode spatial configuration, excitation and sensing methods, and focusing techniques. Additionally, existing systems are incapable of conducting closed loop control of excitation and focusing based on real time data collection, data processing or data storage entirely within a sonde for borehole analysis or as part of a system that is placed at the surface for near surface analysis. Additionally, V&W focusing electrode arrangements require that the electrodes are located a great distance from each other with several electrodes located outside the sonde. Additionally, existing focusing techniques and systems in general are not optimized for low power operation.